1. Field of the Invention
The present invention relates to a mobile communication system which supports the transmission of packet data, and more particularly to an apparatus and a method for allocating identifiers (IDs) which differentiate data to be transmitted.
2. Description of the Related Art
FIG. 1 is a block diagram schematically illustrating a construction of a general mobile communication system.
The mobile communication system is a UMTS (Universal Mobile Terrestrial System) mobile communication system and includes a core network (CN) 100, multiple radio network subsystems (RNSs) 110 and 120, and a user element (UE) 130. Each of the RNSs 110 and 120 includes a radio network controller (RNC) and multiple base stations (node Bs). For instance, the RNS 110 includes an RNC 111, and node Bs 113 and 115, and the RNS 120 includes an RNC 112, and node Bs 114 and 116. Further, each of the RNCs 111 and 112 may be classified as a serving RNC (SRNC), a drift RNC (DRNC), or a controlling RNC (CRNC) according to an operation of each RNC. The SRNC represents an RNC for managing information of each UE and taking charge of data transmission with the CN 100. Further, when data of a UE is transmitted/received to/from an SRNC via another RNC other than the SRNC, the another RNC becomes the DRNC. The CRNC is an RNC for controlling each node B. When the RNC 111 manages the information of the UE 130 in FIG. 1, the RNC 111 operates as an SRNC with respect to the UE 130. Further, when the UE 130 moves and the data of the UE 130 are transceived through the RNC 112, the RNC 112 becomes a DRNC with respect to the UE 130 and the RNC 111 controlling the node B 113 communicating with the UE 130 becomes a CRNC of the node B 113.
The RNC and the node B are connected to each other through an Iub interface, the RNCs are connected to each other through an Iur interface, and the UE and a Universal Terrestrial Radio Access Network (UTRAN) are connected to each other through a Uu interface. The RNC allocates radio resources to multiple node Bs managed by the RNC and the node B provides the UE with radio resources which are allocated by the RNC. These radio resources are provided according to each cell, and radio resources provided by the node B represents radio resources regarding a specific cell controlled by the node B. The UE sets a radio channel by means of the radio resources regarding the specific cell controlled by the node B, and transmits/receives data by means of the set radio channel. Accordingly, since the UE recognizes only a physical channel provided according to (in relation to) each cell (thereof), a differentiation between a node B and a cell has no meaning. Hereinafter, the present invention interchangably uses the terms and node B cell.
In order to support multicasting multimedia communication, there is a broadcast/multicast service providing a service from one data source to a plurality of user equipments (UEs). The broadcast/multicast service may be classified as a cell broadcast service (CBS), a message-centered service, and a multimedia broadcast/multicast service (MBMS) providing multimedia such as a real-time image and voice, a still image, characters, etc.
When an MBMS is provided, it is assumed that the UE is one which wishes to receive the MBMS and the RNCs 111 and 112 transmit the MBMS.
In this case, the RNC 111 and 112 and the UE 130 construct an MBMS radio bearer with respect to the MBMS so as to process MBMS data.
Constructing the MBMS radio bearer means constructing a PDCP (Packet Data Convergence Control) entity, an RLC (Radio Link Control) entity, a Medium Access Control (MAC) entity, and a Physical Layer (PHY) entity for processing MBMS data.
Also, new logical channels called an MBMS traffic channel (MTCH) and an MBMS control channel (MCCH) have been introduced. The MTCH is a logical channel for transmitting user data for a specific MBMS and is constructed such that the number of the MTCH matches with the number of MBMSs provided in a cell. The MCCH is a channel for providing control information relating to an MBMS and one MCCH is constructed for each cell. The MCCH is transmitted using a common channel such as a secondary-common control physical channel (S-CCPCH).
Therefore, when a plurality of MBMSs are provided in a specific cell, the RNC inserts an MBMS identifier into relevant MBMS data and transmits the MBMS data. In this case, the MBMS data into each of which a relevant MBMS identifier is inserted are transmitted through a different S-CCPCH and FACH (Forward Access Channel) from each other.
According to the prior art with respect to this transmission, an identifier having a dedicated value is allocated to each cell.
For example, according to the prior art, while the maximum number of MBMSs which can be simultaneously provided in one cell may change depending on the environment of the cell and the types of services, 16 bits are allocated to an MBMS ID field for a dedicated identifier used in one cell, from the viewpoint of sufficiently providing reserve values.
However, when one identifier having a unique feature corresponding to a cell unit is allocated to each cell, the number of distinguishable MBMSs is limited to a small value. In other words, the prior art must transmit excessive information through a radio channel in order to differentiate service-available MBMSs. As a result, in the prior art limited radio resources are inefficiently used.
Therefore, in order to solve such a problem, it is necessary to provide a new method capable of allocating MBMS identifiers.